(1) Field of the Invention
The present invention relates to a process for preparing a Diels-Alder addition product of a conjugated diolefin and acrylonitrile by reacting the conjugated diolefin with acrylonitrile.
(2) Description of the Related Art
It is known to prepare a Diels-Alder addition product of a conjugated diolefin and acrylonitrile by reacting the conjugated diolefin with acrylonitrile. This is a thermal reaction and thus is desirably conducted at elevated temperatures. However, when the reaction is carried out at a high temperature, an increased amount of polymers are formed in the reaction solution.
These polymers can be insoluble in the reaction solution and can adhere to or deposit on inner surfaces at or around an inlet of feed and an outlet of the reaction solution. This interferes with the operation of the reaction. Thus, processes have been proposed which add various polymerization inhibitors to the reaction solution to inhibit the by-production of these polymers and to thereby avoid the above-mentioned problems. In order to avoid polymerization of the diolefin or olefin used in a Diels-Alder reaction, the following processes are known: Japanese Patent Publication No. 54-9198 discloses the use of an N-nitrosoamine compound; Japanese Patent Laid-Open No. 61-165338 discloses the use of an alkylphenol compound; Japanese Patent Publication No. 57-7131discloses the use of a p-phenylenediamine compound; and Japanese Patent Laid-Open No. 62-167733 discloses the use of a hydroxylamine compound.
Alternatively, in a process for preparing cyanonorbornene through a Diels-Alder reaction between acrylonitrile and a conjugated diolefin that is produced from dicyclopentadiene, Japanese Patent Laid-Open No. 7-188147 discloses performing the reaction in the presence of an N-nitrosoamine compound, and Japanese Patent Publication No. 59-51533 discloses adding cyanonorbornene before adding raw material of the reaction.
Japanese Patent Laid-Open No. 51-34139 proposes a process for keeping the raw material in a liquid phase by feeding the raw material into the reaction solution through a lower portion of the reactor and taking out the reaction solution through an upper portion of the reactor to achieve reaction under a pressure higher than a pressure generated spontaneously during the reaction at a given temperature, as a way of improving the yield of cyanonorbornene while reducing the amount of by-produced polymers in a reaction between dicyclopentadiene and acrylonitrile.
Studies made by the present inventors have revealed that the reaction between a conjugated diolefin and acrylonitrile may tend to produce a highly insoluble polymer in the reactor or in the inlet or outlet pipe of the reactor, or may sometimes be accompanied by danger, depending on the methods and aspects used.
More specifically, the present inventors have carried out various reactions using both a so-called tubular reactor in which the conjugated diolefin and acrylonitrile are heated and reacted in a spiral pipe, and a vessel type reactor. In the so-called tubular reactor, it was found that insoluble polymers adhere to the inner surface of the pipe which may then clog the pipe. Thus, this process is hardly applicable to continuous production.
On the other hand, the vessel type reactor does not suffer from adhesion of the insoluble polymers to the inner surface thereof when the reaction is carried out with the reactor completely filled with a solution. However, the present inventors have found that this process is quite dangerous because of sudden change in pressure in the reactor. The present inventors have also found that this process can produce insoluble polymers which adhere to pipes through which the raw material is supplied to the reaction solution or to a discharge portion of the pipes and create a possibility of clogging the pipes. The process described in the above-mentioned Japanese Patent Laid-Open No. 51-34139 is thus revealed to be effective as a process for improving the yield of cyanonorbornene while reducing the by-produced amount of the polymers, but such process is far from being a safe.
As described above, there are some conventional processes that are directed to inhibiting the production of insoluble polymers in the reaction solution during the reaction. However, there is no description of a reactor that can effectively inhibit production of the insoluble polymers. Nor is there a description of a process for carrying out the reaction in a safe manner.